Transaction verification threads locks

[NikVolf]

Out of 10% total, in every transaction verification threads there are plenty time spent on locks (18% of 100%):

This is obviously rayon-only code

Unsure why it needs to wait on anything, @debris?

Running Time	Self (ms)		Symbol Name
4040.0ms    0.9%	108,0	 	        _pthread_mutex_lock_wait
3932.0ms    0.9%	3932,0	 	         __psynch_mutexwait
3022.0ms    0.7%	16,0	 	        _pthread_mutex_unlock_drop

[debris]

We have recently updated ryon from 0.4 to 0.6. Would be good to check if the problem still exists